The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

Online terror fight on G20 agenda: PM

Malcolm Turnbull predicts tackling terrorism in cyberspace will be high on the agenda for the G20 summit in Germany.

The prime minister will join US President Donald Trump, Russian President Vladimir Putin and other world leaders in Hamburg for the annual talks next week.

Host leader German Chancellor Angela Merkel has flagged a discussion on how to better harness social media platforms such as Facebook and Twitter to combat terrorism and the spread of extremism.

"This has become a major problem for our law enforcement and security agencies, not just in Australia but right around the world," Mr Turnbull told reporters in Melbourne on Monday.

"It is one of those problems that requires concerted international action."

Cyberspace could not be "ungoverned space", he said.

"The law must prevail and security must prevail on the internet as it does everywhere else. This is a big challenge for leaders at the G20 and I look forward to arguing that case strongly in order to protect our citizens and citizens of every other nation."

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Security will be tight in Hamburg, with 20,000 police officers being brought in to handle protests and ensure the July 6-7 summit is not disrupted by terrorists.

Anti-capitalism protesters will vie for attention with a planned demonstration against Turkish President Tayyip Erdogan by supporters of the outlawed Kurdistan Workers Party and pro-Erdogan Turkish nationalists.

However, a more peaceful crowd is expected on the eve of the summit at a free Global Citizen Festival concert featuring Coldplay, Shakira and Pharrell Williams.

Chancellor Merkel has also put free and fair trade, climate, refugees and steel industry overcapacity on the summit's agenda.

G20 members account for 86 per cent of the world economy, 78 per cent of global trade, and two-thirds of the world's population, including more than half of the world's poor.